The present invention relates to a piston ring, and a method of making a piston ring.
As is known, a piston ring is located in a piston ring groove in a piston which moves in a cylinder. In an internal combustion engine, fuel is directed into the cylinder and ignited to move the piston in the cylinder. The expanding gases created by the ignited fuel force the piston in a power stroke.
Traditionally, a piston carries a compression ring which is located adjacent the surface against which the expanding gases act. The compression ring functions to block flow of the gases between the piston and cylinder in order to maximize the gases acting directly on the piston to move it. Of course, any blow-by, i.e., flow of gases past the piston ring, minimizes the force acting to move the piston in the power stroke and thereby detrimentally affects fuel efficiency.
Typically, compression piston rings are located in a tapered piston ring groove at the upper end of the piston. The sidewalls of the piston ring are subject to substantial wear during piston movement. The wear on the sidewalls of a compression piston ring is greatest at a location generally adjacent the outer periphery of the piston and the side wear is at a minimum at the inner periphery of the compression piston ring.
Techniques have been utilized in order to minimize side wear of the piston ring. These techniques have involved providing a hardened surface on the sidewalls of the piston ring. Such is accomplished by hardening the entire piston ring blank by a conventional heat treatment. This, of course, has resulted in the entire outer periphery of the piston ring blank being hardened including the entire sidewall surface. After hardening, the blank is machined. Such machining includes turning a groove, for receiving a wear coating, in the outer periphery of the ring, milling a gap in the ring, etc. These machining steps were performed after hardening because if performed before hardening, the heat treatment for hardening would affect the machined areas and cause distortion, etc. This, however, has created machining difficulties because hardened piston ring blanks are difficult to machine.
Further, because the entire periphery of the ring was hardened, the edges of corners of the piston ring, particularly the edges adjacent the surface which is to engage the cylinder bore were subject to nicking during handling and/or assembly. Such nicking creates stress-risers and fatigue cracks result. Such stress-risers and fatigue cracks greatly affect the efficiency and effectiveness of the piston ring and result in blow-by occurring and/or ring breakage.
The present invention is directed to a piston ring which is not susceptible to nicking at the edges. Further, the piston ring of the present invention may be made by a process which does not require machining of a hardened ring. Thus, the present invention is more effective than the prior art piston rings, and can be manufactured without the machining problems encountered in machining a hardened piston ring blank.
Specifically, the present invention is directed to a piston ring which has side surfaces hardened in a localized area intermediate the radial extent of the respective side surfaces. Thus, the problem of fatigue cracks which occur at the intersection of the side surfaces and the outer peripheral wall of the piston ring which engages the cylinder bore is minimized. Also the piston ring of the present invention has a relatively soft material area at the outer periphery of the piston ring which is adjacent the outer periphery of the piston. As a result, the softer material of the piston ring may seat during initial operation of the piston against the piston and provide an effective seal. This, of course, also minimizes the possibility of blow-by.
Further, the localized areas of the side surfaces of the piston ring of the present invention are hardened after the piston ring blank is machined. Specifically, the piston ring of the present invention is made of cast iron material or steel strip material. The material is formed into a ring. After the material is formed, other manufacturing operations are performed on the ring. For example, the ring is turned (i.e., machined) in order to provide a groove on the outer periphery of the ring for receipt of a wear material which is bonded to the ring material and engages the bore of the cylinder. Also, the ring is milled in order to mill a gap into the ring.
All of the above machining steps occur prior to hardening of the localized areas of the side surfaces of the ring. The localized areas of the side surfaces of the piston ring are hardened by a laser technique. The ring is moved into a position adjacent a laser beam and the ring is rotated at a predetermined speed relative to the laser beam. An annular band of hardened material on the side surface of the ring results. The hardening occurs due to the fact that the laser beam heats the material of the ring to above the critical temperature. The heat conduction of the base material and a supplementary water quench lowers the temperature at a critical rate to provide hardened martinsite, which material solidifies after passing the laser beam. There is no distortion of the ring. Both side surfaces of the ring are hardened by rotating the ring relative to a laser beam.
Accordingly, the piston ring of the present invention not only has a hard side surface in order to minimize side wear of the piston ring as is conventional but also is constructed to minimize the possibility of cracks at the corner of the piston ring adjacent the cylinder wall in which the piston moves which cracks greatly increase the possibility of ring breakage and blow-by. Further, the present invention provides a relatively soft material on the sidewall of the piston ring adjacent the corner of the piston ring groove at the outer periphery of the piston so as to enable the piston and ring to seat together and thereby provide an effective seal therebetween. Finally, the piston ring of the present invention may be manufactured by a technique which greatly simplifies machining of the piston ring.